1. Field of the Invention
This invention relates to the in situ generation and incorporation of polyurethane prepolymers generated within a matrix of bituminous material such as asphalt. The resulting bituminous polyurethane interpenetrating elastomeric network compositions can be applied as coatings and sealants for roofing, coverings, and construction waterproofing applications, as well as other applications.
2. Description of Related Art
Polyurethanes are extensively used as coatings and sealants in housing, construction, furniture, and other industries. Polyurethane prepolymers are generally developed by reacting different polyols with di- or poly-isocyanates in varying ratios. FIG. 2 depicts a reaction between a polyol and diisocyanate. Polyurethanes are hard, water-resistant, slippery when wet, and tend to degenerate when exposed to ultra-violet light.
"Bituminous material" is meant to include bitumen, asphalt, coal tar, and performance-rated asphalt. Due to the low cost of bituminous material, its relatively high penetration value when applied to most porous surfaces, weather-resistant nature, and impermeability to water, bituminous material has traditionally been used as a main component of protective films, adhesive binders in asphalt emulsions (M. Lalanne and J. Serfass, U.S. Pat. No. 4,724,245), in blends used for paving and roofing, joint sealants, paints, and other end uses. Existing unreinforced bituminous materials tend to crack during normal seasonal thermal expansion. In addition, typical bituminous materials are difficult to apply and take a long time (days) to cure completely.
Attempts to provide a blend of a liquid, preferably an ambient-curable prepolymer, with bituminous material have been made (H. Lucke, U.S. Pat. No. 4,871,792). In the past, several methods were developed to increase the compatibility between the bituminous binder and polyurethanes, either by using a modified clay (R. J. Janoski, U.S. Pat. Nos. 5,421,876 and 5,319,008), or pre-treating the bituminous materials before mixing with polyurethane prepolymer (M. Shihadeh, U.S. Pat. No. 3,980,597).
Several attempts to develop a rubberized bituminous material using crumb rubber have also been made. Methods are available, reported, and in practice today. Crumb rubber from recycled car and truck tires improves wear resistance (D. W. Causyn and K. Thys, PCT Int. Appl. WO 9221820), lowers temperature fracture properties (G. R. Morrison and S. A. M. Hesp., J. Mater. Sci. 30(10), 2584 (1995) and A. Coomaraswamy, S. Manolis and S. Hesp., Am. Chem. Soc. Div. Fuel. Chem., 41(4), 1322 (1996)); and enhances coating performance and safety of the coated surface (M. Wm. Rouse, Rubber World, 212(2), 23 (1995)). Most of these applications are used in the paving industry, anti-skid mats for playgrounds, and running tracks (H. L. Draper, D. F. Levy, and D. W. Gagle, U.S. Pat. No. 3,547,674).
Apart from the use of crumb rubber, other polymers are used to modify asphalt (M. E. Labib, G. M. Memon, and B. H. Chollar, Prepr. Pap.--Am. Chem. Soc., Div. Fuel. Chem., 41(4), 1209 (1996), I. K. Negulescu and W. H. Daly, Annu. Tech. Conf., Soc. Plat. Eng. 54th (vol. 1), 1175 (1996). The thermoplastic nature of these existing polymer modified bituminous materials limits their coating and sealant applications.
These past attempts to incorporate a resin within a bituminous material have failed for a combination of reasons. First, polyurethanes and bituminous materials are not miscible because polyurethanes are polar, while bituminous materials are non-polar. Second, without more, the reaction rate between the reagents forming the polyurethane (polyol and isocyanate) is slow enough that the reagents separate from the bituminous material, polymerize, and form non-integrated, heterogenous products. These heterogenous products do not produce synergistic qualities such as increased strength and ease of application.